Various brominated aromatics are known flame retardants for thermoplastics. For example, brominated polystyrenes are accepted as commercially significant flame retardants for use in a variety of thermoplastics. These brominated flame retardants have a high aromatic bromine content and, to the extent possible, a low thermally labile bromine content. However, a high aromatic bromine content can be accompanied by a higher than desired thermally labile bromine content. The thermally labile bromine content of a brominated flame retardant is determined by measurement of the HBr off-gas generated when the flame retardant is heated at an elevated temperature for a period of time. The thermally labile bromine content is dependent on (a) the content of HBr by-product still entrapped in the flame retardant (even after finishing steps to reduce this content) and (b) the amount of molecular, non-aromatic bromine present. Examples of non-aromatic bromine are aliphatic bromides, where the aliphatic group is either an alkylene or alkylidene group serving as a bridging group between aromatic groups or is an alkyl substituent on an aromatic group. No matter the source, HBr off-gas from the flame retardant used in the thermoplastic formulations can result in damage to molding equipment used to fabricate thermoplastic formulations at elevated temperatures into articles, e.g., TV enclosures and the like. Thus, there is a need to have a brominated flame retardant having a low thermally labile bromine content.
Fortunately, the amount of entrapped HBr can be and is significantly reduced by water quenching the crude flame retardant reaction mass, followed, as needed, by further finishing treatment, be it by chemical treatment or by water washing. Usually, the removal of entrapped HBr is effective and thus, its contribution to the thermally labile bromine content of the finished brominated flame retardant product is not significant.
Reduction of the other source of HBr off-gas, i.e., the chemically bonded molecular non-aromatic bromide, is more problematic. There are few satisfactory options available in as much as the techniques used for entrapped HBr reduction are of minimal use against the much more stubborn non-aromatic bromine. In the case of brominated styrenic polymers it has been possible, by ingenuously modifying the bromination process parameters and reactant feeds, to diminish the formation of non-aromatic bromine as is evidenced by HP 7010 and HP 3010 flame retardant products of Albemarle Corporation. These commercial products exhibit a thermally labile bromine content of less than 500 ppm while still providing up to about 68 wt % of aromatic bromine in the product.
It would be a desirable contribution to the art if a way could be found of providing new highly aromatic, relatively low molecular weight hydrocarbon raw materials that can be effectively brominated to form brominated flame retardants that exhibit a very high aromatic bromine content (i.e., >72 wt % of bromine), but which at the same time, have a commercially acceptable low thermally labile bromine content.
This invention is deemed to provide such a contribution to the art.